A liquid crystal display device used for a liquid crystal television, a liquid crystal display, etc. usually has a liquid crystal alignment film to control the liquid crystal alignment state provided therein. As the liquid crystal alignment film, a polyimide liquid crystal alignment film obtained by applying a liquid crystal aligning agent containing as the main component a solution of a polyimide precursor such as a polyamic acid (polyamide acid) or a soluble polyimide to a glass substrate or the like and baking it is mainly used. At present, by the industrially most common method, a liquid crystal alignment film is prepared by carrying out so-called rubbing treatment such that the surface of a polyimide liquid crystal alignment film formed on an electrode substrate is rubbed in one direction with a cloth of e.g. cotton, nylon or polyester.
As an alternative to the rubbing treatment, a photo-alignment method of imparting liquid crystal alignment performance by irradiation with polarized ultraviolet rays has been known. As the liquid crystal alignment treatment by the photo-alignment method, in terms of mechanism, one utilizing photoisomerization reaction, one utilizing photocrosslinking reaction, one utilizing photodecomposition reaction, etc. have been proposed (Non-Patent Document 1). Further, in Patent Document 1, use of a polyimide film having an alicyclic structure such as a cyclobutane ring in its main chain for photo-alignment method has been proposed.
Along with a tendency to high precision of a liquid crystal display device, from demands for suppression of a decrease in the contrast of the liquid crystal display device and a reduction of a residual image, for a liquid crystal alignment film, not only development of an excellent liquid crystal alignment property and a stable pretilt angle is required, but also properties such as a high voltage retention, suppression of a residual image which occurs due to alternating-current drive, a low residual charge when a direct-current voltage is applied, and/or quick relaxation of the residual charge accumulated by a direct-current voltage, become more important. For a polyimide liquid crystal alignment film, in order to meet the above demands, various proposals have been made (Patent Documents 2 to 6).